Riding the bicycle

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Riding the bicycle

Much of my forthcoming book is steeped in insights about evolution that have been derived from the new paleobiological synthesis, and in doing a bit a background reading I came across an interesting tidbit.

In 1980 numerous authorities on evolutionary science converged in Chicago for a conference on macroevolution. Spurred by the work of paleontologists such as Niles Eldredge, Stephen Jay Gould, David Raup, and Steven Stanley, the meeting's goal was to assess whether the traditional slow-and-steady model of evolution preferred by geneticists fit what paleontologists saw in the fossil record. The general feeling among paleontologists, at least, was that there was more to evolutionary change than what lab workers were seeing in fly bottles. The fossil record did not portray a uniform process by which species were constantly accumulating adaptations through point mutations plus selection. A more common trend was a rapid burst of change (i.e. speciation) followed by stasis.

Unfortunately there were no plans to produce a book presenting the meeting's proceedings, but journalist Roger Lewin described some of the transactions for the journal Science. Of particular interest were the reactions of some of the old guard of the Modern Synthesis. They held fast to their positions and suggested that the paleontologists were merely reinventing the wheel; the architects of the earlier evolutionary synthesis had already considered and dismissed the ideas about contingency and constraint being forwarded. Lewin wrote;

The outcome of all this [George Oster's presentation on development] was the proposal of a hierarchy of processes and constraints linking possible genotypes with actual phenotypes: instructions encoded in the genetic library are filtered through a net of developmental constraints, giving rise to a set of possible phenotypes; it is at this stage that natural selection works, limiting the surviving phenotypes to those with suitable adaptive features. The omnipotent position of adaptationism embodied in the Modern Synthesis is overturned.At this point in the discussion [John] Maynard Smith felt moved to protest: "These structuralist ideas are presented as if they are antagonistic to the Modern Synthesis. In fact, you will find the major ideas here in a book I wrote 25 years ago and in the writing of many others in the tradition of the Modern Synthesis," he said, adding with obvious concern, "You are in danger of preventing understanding by suggesting that there is intellectual antagonism where none exists.""You may have had the wheel, John, but you didn't ride away on it," Oster quipped with a telling metaphor. [Stephen Jay] Gould added in more serious vein: "It is not so much what is said that counts, but what is done. These phenomena we talk about may have been acknowledged in the Modern Synthesis, but the principle guiding all the work of the past few decades has been adaptationism."

Indeed, contrary to the protestations of Maynard Smith the paleontologists were raising important questions about what had been previously assumed about evolutionary change. Maybe previous workers had been recognized these issues but, for whatever reason, little had been done about them. The paleobiological synthesis that began to emerge during that time fed upon such problems.

Whether or not neontologists have truly welcomed paleontologists to the theoretical "high table" during the past thirty years is debatable, but Lewin's account of the Maynard Smith/Oster exchange struck me for for a different reason. In many popular portrayals of evolution the contributions of paleontology still take a backseat to genetics; thanks for the fossils, but don't worry so much about the theory next time. Authors seem grateful that there are fossils with transitional features to demonstrate the fact of evolution yet evolution is still often presented as being a uniformitarian march from simple to complex. Considerations of contingency, constraint, differing levels of selection, punctuated equilibria, and other products of the paleobiological synthesis rarely get so much as a nod, and if they do it is simply to affirm that they do not offer anything not anticipated by a Modern Synthesis-type view of evolution as near-infinite possibilities whittled down by selection.

I certainly cannot compete with the popular work of Stephen Jay Gould, but I hope to at least stir in a little more interest in the theoretical contributions of paleontology in Written in Stone. There is much more to talk about than just transitional fossils and fossil succession. I have no doubt that some who prefer a more law-like and predictable version of evolution will be irritated by my approach, but where would we be if we only thought about what made us most comfortable?